This invention relates generally to energy storing devices, and more particularly, to an apparatus and method for improving the performance of a thin-film electrochemical generator.
The demand for new and improved electronic and electro-mechanical systems has placed increased pressure on the manufacturers of energy storing devices to develop battery technologies that provide for high energy generation in a low-volume package. Conventional battery systems, such as those that utilize lead acid for example, are often unsuitable for use in high-power, low-weight applications. Other known battery technologies may be considered too unstable or hazardous for use in consumer product applications.
A number of advanced battery technologies have recently been developed, such as metal hydride (e.g., Nixe2x80x94MH), lithium-ion, and lithium polymer cell technologies, which would appear to provide the requisite level of energy production and safety margins for many commercial and consumer applications. Such advanced battery technologies, however, often exhibit characteristics that provide challenges for the manufacturers of advanced energy storage devices.
For example, such advanced power generating is systems typically produce a significant amount of heat which, if not properly dissipated, can result in a thermal runaway condition and eventual destruction of the cells, as well as the system being powered by the cells. The thermal characteristics of an advanced battery cell must therefore be understood and appropriately considered when designing a battery system suitable for use in commercial and consumer devices and systems. A conventional approach of providing a heat transfer mechanism external to such a cell, for example, may be inadequate to effectively dissipate heat from internal portions of the cell. Such conventional approaches may also be too expensive or bulky in certain applications. The severity of consequences resulting from short-circuit and thermal run-away conditions increases significantly when advanced high-energy electrochemical cells are implicated.
Other characteristics of advanced battery technologies provide additional challenges for the designers of advanced energy storage devices. For example, certain advanced cell structures are subject to cyclical changes in volume as a consequence of variations in the state of charge of the cell. The total volume of such a cell may vary as much as five to six percent or more during charge and discharge cycling. Such repetitive changes in the physical size of a cell significantly complicates the mechanical housing design and the thermal management strategy. Thee electrochemical, thermal, and mechanical characteristics of an advanced battery cell must therefore be understood and appropriately considered when designing an energy storage system suitable for use in commercial and consumer devices and systems.
There is a need in the advanced battery manufacturing industry for an electrochemical generator that exhibits high-energy output and good heat transfer characteristics and one that provides for safe and reliable use in a wide range of applications. There exists a further need for a packaging configuration which accommodates the unique dynamics of an electrochemical cell which is subject to volumetric changes during charge and discharge cycling. The present invention fulfills these and other needs.
The present invention is directed to an improved electrochemical generator. The electrochemical generator includes a thin-film electrochemical cell which is maintained in a state of compression through use of an internal or an external pressure apparatus. A thermal conductor, which is connected to at least one of the positive or negative contacts of the cell, conducts current into and out of the cell and also conducts thermal energy between the cell and thermally conductive, electrically resistive material disposed on a vessel wall adjacent the conductor. The thermally conductive, electrically resistive material may include an anodized coating or a thin sheet of a plastic, mineral-based material or conductive polymer material. The thermal conductor is fabricated to include a resilient portion which expands and contracts to maintain mechanical contact between the cell and the thermally conductive material in the presence of relative movement between the cell and the wall structure. The electrochemical generator may be disposed in a hermetically sealed housing.